The underlying problem in the case this article describes is one of classification. Fact checking every claim is a lot of work, so fact checkers find a widely-

The underlying problem in the case this article describes is one of classification. Fact checking every claim is a lot of work, so fact checkers find a widely-circulating claim to check and generalize it from whatever various specific claims are in circulation. In this case, it was generalized to "there's no science behind masks on kids". That claim is easy to check, and it's false; there are multiple scientific studies showing that requiring masks in schools reduce covid rates among students. The author's article did not make that claim or anything that could be reasonably reduced to "there's no science behind masks on kids". Instead, his claim was that the CDC made a recommendation based on a specific study, and that the study in question has serious methodological flaws (the headline phrase "junk science" is a bit sensational). That's a more narrow claim, most of which probably falls into the category of opinion or analysis rather than fact-checking.